1. Field of the Invention
The present invention relates to a patterning process by a multilayer resist method used for microfabrication in a step of producing a semiconductor device.
2. Description of the Related Art
As exposure light used for formation of a resist pattern, light exposure using g-beam (436 nm) or i-beam (365 nm) from a mercury lamp as a light source was widely used in 1980s. A method for shifting to a shorter wavelength of exposure light was considered to be effective as the means for further miniaturization. As a result, in the mass production process after DRAM (Dynamic Random Access Memories) with 64 MB (processing feature size: 0.25 μm or less) in 1990s, the exposure light source of i-beam (365 nm) was replaced by a KrF excimer laser having a shorter wavelength of 248 nm. However, for production of DRAM with an integration degree of 256 MB and 1 GB or more requiring miniaturized process technologies (processing feature size: 0.2 μm or less), a shorter wavelength light source was required. Over a decade, photolithography using an ArF excimer laser (193 nm) has been fully investigated. At first, it was expected that the ArF lithography would be applied to the production of 180-nm node devices. However, the KrF excimer lithography lived long to the mass production of 130-nm node devices. The full-fledged application of ArF lithography started from the 90-nm node. Further, the ArF lithography combined with a lens having an increased NA of 0.9 has been applied to the mass production of 65-nm node devices. The next 45-nm node devices has required an advancement to shift to a shorter wavelength of exposure light, and the F2 lithography having a wavelength of 157 nm has become a candidate. However, there are many problems in an F2 lithography; an increase in cost of a scanner due to the use of a large quantity of expensive CaF2 single crystals for a projector lens, extremely poor sustainability of a soft pellicle, which leads to a change of an optical system due to introduction of a hard pellicle, a decrease in an etching resistance of a resist film, and the like. For these various problems, the development of F2 lithography has been stopped and ArF immersion lithography has been introduced.
In the ArF immersion lithography, the space between a projection lens and a wafer is filled with water having a refractive index of 1.44 by a partial filling manner. This enables high-speed scanning. A lens having a NA of 1.3 is applied to mass production of 45-nm node devices.
One of the candidates for 32-nm node lithography technique is extreme ultraviolet (EUV) lithography having a wavelength of 13.5 nm. Then, exemplary objects accompanying to the EUV lithography are to increase an output of laser, enhance a sensitivity of resist film, enhance a resolution, decrease a line edge roughness (LER), achieve a defect-free MoSi laminate mask, lower aberrations of a reflecting mirror, for example, thereby leaving a pile of objects to be attained. The development of a high refractive index liquid immersion lithography which is another candidate for the 32-nm node lithography has been stopped since the transmittance of LUAG which is a candidate for a high refractive index lens is low and the refractive index of liquid does not achieve a desired value of 1.8. As described above, light exposure used as the general purpose technology approaches the limit of essential resolution introduced by the wavelength of a light source.
One of miniaturized process technologies that draw attention in recent years is a double patterning process involving performing a first set of exposure and development to form a first pattern and performing a second set of exposure and development to form a pattern between features of the first pattern (Non-patent document 1). A large number of processes are proposed as the double patterning process. For example, there is a process involving performing a first set of exposure and development to form a photoresist pattern having line-and-space at intervals of 1:3, processing the underlying hard mask by dry etching, applying another hard mask thereto, performing a second set of exposure and development of a photoresist film to form a line pattern in the spaces of the first exposure, and processing the hard mask by dry etching, thereby forming a line-and-space pattern at a half pitch of the first pattern. An another process involves performing a first set of exposure and development to form a photoresist pattern having spaces and lines at intervals of 1:3, processing the underlying layer of hard mask by dry etching, applying a photoresist film thereto, performing a second set of exposure and development to form a second space pattern on the remaining hard mask portion, and processing the hard mask by dry etching. While the former process requires two applications of hard mask, the latter process uses one layer of hard mask but requires to form a trench pattern which is difficult to resolve as compared with the line pattern. In both the processes, the hard mask is processed by two dry etchings.
As the other finer patterning technology, a process involving forming a line pattern in the X direction on a positive resist film by dipole illumination, hardening the resist pattern, applying a resist composition thereto, exposing the line pattern in the Y direction to dipole illumination, and forming a hole pattern from gaps of a lattice line pattern (Non-patent document 2) is proposed.
As one of methods for transferring a lithography pattern onto a substrate using a hard mask as described above, there is a multilayer resist method. The multilayer resist method involves interposing an middle layer film having a different selectivity, for example, a silicon-containing resist underlayer film, between a photoresist film, that is, a resist upper layer film, and a substrate to be processed, forming a pattern on the resist upper layer film, transferring the pattern onto the resist underlayer film using the resist upper layer film as an etching mask, and transferring the pattern onto the substrate to be processed using the resist underlayer film as an etching mask.
As a composition for an underlayer film used in such a multilayer resist method, a composition for forming a silicon-containing film is well known. Examples thereof include a silicon-containing inorganic film, a SiO2 film (Patent document 1) and a SiON film (Patent document 2), which are obtained by CVD, and a spin on glass (SOG) film (Patent document 3) and a crosslinkable silsesquioxane film (Patent document 4), which are obtained by spin-coating.
The lithography characteristics and stability of a composition for forming a silicon-containing resist underlayer film have been investigated. Patent document 5 discloses that when a composition for forming a resist underlayer film containing a thermal crosslinking accelerator is prepared, a resist underlayer film having good etching selectivity and storage stability is provided. However, as the finer patterning of a semiconductor device is promoted, the line width of the pattern is reduced, and the film thickness of a resist upper layer film is reduced to prevent pattern fall. Therefore, improved adhesion and etching selectivity in the finer pattern than the conventional patterns are required in performances needed in a resist underlayer film.
Most of a coating film practically used in the conventional multilayer resist method has been an organic film and the silicon-containing film as described above. However, in a process for producing a semiconductor device in a marginal domain of lithography by the recent light exposure, a complicated process such as the double patterning process has been proposed. Therefore, it is difficult to construct a reasonable production process using only the conventional organic film and a silicon-containing film. In order to construct a more reasonable production process of a semiconductor device, it is required that a coating film which has an etching selectivity to both film components of an organic film and a silicon-containing film, and can be separated under a mild condition without causing damage to the substrate after exhibiting an etching mask function which is one of functions of the underlayer film, that is, after pattern-transferring from the underlayer film.